I. Field of the Invention
The present invention relates to a method for forming a panel, such as an automotive panel, by the resin transfer molding process.
II. Description of the Prior Art
Automotive panels, such as the quarter panels, rear deck, hood and the like, are typically manufactured from metal stampings which are subsequently welded together in order to form the desired panel. This process for forming automotive panels is relatively inexpensive when a large number of panels are made from a single stamping since the cost of the stamping is amortized over the number of stampings made.
However, there are a number of automotive vehicles manufactured today which are manufactured in relatively limited quantities, for example 20,000 or 30,000 vehicles. For such vehicles, the amortization cost of the metal stampings necessary to form the various automotive panels significantly increases the overall cost of the vehicle. In some cases, the manufacture of the limited quantity vehicle is almost prohibitive due to the high cost of the tooling necessary to make the stampings for the various automotive panels.
One relatively new process to reduce the cost of manufacturing the automotive panels for limited quantity vehicles has been developed for constructing the vehicle panels out of glass fibers, rather than metal. The material cost for such panels is higher than the cost for a metal panel, but the tooling costs are substantially lower.
In these previously known fiber panels, a matting of glass fibers is simply positioned within the mold and the mold is then injected with a settable resin which, when hardened, forms the panel. These previously known methods for forming the automotive panels, however, have not proven wholly satisfactory in operation.
One disadvantage of the previously known methods for forming the automotive panels is that the panel has a relatively rough outer texture when formed. In many cases, the cosmetic defects on the panel require that the panel be scrapped.
In addition, many of these previously known panels are relatively heavy in construction and thus unnecessarily increase the overall weight of the vehicle. Attempts to construct a vehicle panel from two sheets of glass fibers with a lightweight core positioned therebetween have not proven wholly successful since shrinkage lines appear on the panel where the two sheets of glass fibers contact each other. Such lines are caused by uneven shrinkage between the two sheets of glass fibers.